Device with a High Efficiency Voltage Multiplier

ABSTRACT

A device includes a capacitive element that is coupled between first and second nodes and that includes a first well region, a second well region, and a transistor. The second well region is formed in the first well region, has a different conductivity type than the first well region, and is coupled to the second node. The transistor includes source and drain regions formed in the second well region and coupled to each other and to the second node, a channel region between the source and drain regions, and a gate region over the channel region. The first well region and the gate region are coupled to each other and to the first node, whereby a capacitance of the capacitive element is increased without substantially enlarging a physical size of the capacitive element.

BACKGROUND

A device uses a voltage multiplier to generate a voltage higher than,e.g., twice, a supply voltage. For example, a device, such as a memorydevice, may read a memory cell at a read voltage equal to the supplyvoltage and write to the memory cell at a write voltage twice the supplyvoltage.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a schematic diagram illustrating an exemplary device inaccordance with some embodiments.

FIG. 2 is a schematic diagram illustrating the relationship betweenfirst and second clock signals in accordance with some embodiments.

FIG. 3 is a flow chart illustrating an exemplary method of operation ofa device in accordance with some embodiments.

FIG. 4 is a schematic sectional view illustrating an exemplarycapacitive element in accordance with some embodiments.

FIG. 5 is a schematic diagram illustrating an equivalent circuit of acapacitive element in accordance with some embodiments.

FIG. 6 is a schematic diagram illustrating an exemplary device inaccordance with some embodiments.

FIG. 7 is a flow chart illustrating an exemplary method of operation ofa device in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The present disclosure provides a device, e.g., an integrated circuit,that in an exemplary embodiment includes a voltage multiplier, e.g.,voltage multiplier 140 of FIG. 1. The voltage multiplier 140 iscontrolled by first and second clock signals, e.g., first and secondclock signals (CLK1, CLK2) in FIG. 2, so as to generate a load voltage,e.g., 0.8V, higher than, e.g., about twice, a supply voltage, e.g.,0.4V, for driving a load. The voltage multiplier 140 includes a firstcapacitive element (C1). Efficiency of the voltage multiplier 140 can beimproved by increasing a capacitance of the first capacitive element(C1), e.g., via capacitive element construction.

In further detail, FIG. 1 is a schematic diagram illustrating anexemplary device 100 in accordance with some embodiments. The exampledevice 100 includes a supply node 110, a reference node 120, a load node130, and a voltage multiplier 140. The supply node 110 is configured toreceive a supply voltage (Vdd), e.g., 0.4V. The reference node 120 isconfigured to receive a reference voltage (Vss), e.g., 0V, lower thanthe supply voltage (Vdd). The voltage multiplier 140 includes first andsecond nodes (N1, N2), first and second capacitive elements (C1, C2),first and second switch units 150, 160.

The first capacitive element (C1), e.g., a metal-oxide semiconductorcapacitor (MOSCAP), a metal-insulator-metal (MIM) capacitor, or othertype of capacitor, is connected between the first and second nodes (N1,N2). The first switch unit 150 includes first and second switches (SW1,SW2) and is configured to receive a first clock signal (CLK1) thatcontrols operations of the first and second switches (SW1, SW2). Thefirst switch (SW1) is connected between the supply node 110 and thefirst node (N1) and is operable so as to selectively connect anddisconnect the first node (N1) to and from the supply node 110. Thesecond switch (SW2) is connected between the second node (N2) and thereference node 120 and is operable so as to selectively connect anddisconnect the second node (N2) to and from the reference node 120.

Similarly, the second switch unit 160 includes third and fourth switches(SW3, SW4) and is configured to receive a second clock signal (CLK2)that controls operations of the third and fourth switches (SW3, SW4).The third switch (SW3) is connected between the supply node 110 and thesecond node (N2) and is operable so as to selectively connect anddisconnect the second node (N2) to and from the supply node 110. Thefourth switch (SW4) is connected between the first node (N1) and theload node 130 and is operable so as to selectively connect anddisconnect the first node (N1) to and from the load node 130. In thisembodiment, the switches (SW1-SW4) are n-type field-effect transistors(FETs). In some embodiments, one of the switches (SW1-SW4) is a p-typeFET. In other embodiments, one of the switches (SW1-SW4) is any sort oftransistor, e.g., a bipolar junction transistors (BJT), or other type ofswitch.

The second capacitive element (C2), e.g., a MOSCAP, a MIM capacitor, orother type of capacitor, is connected between the load node 130 and thereference node 120.

A load 190 is connected across the second capacitive element (C2). Theload 190 is, in an exemplary embodiment, a time-to-digital converter(TDC) that converts time information into a digital code. For example,the TDC 190 may output a series of 1's and 0's indicating levels ofsignals at a certain point in time. Such a circuit may be useful in anall-digital phase lock loop (ADPLL) system. In some embodiments, thedevice 100 includes the load 190. In other embodiments, the device 100does not include the load 190 and the load 190 may be connected to theload node 130 externally of the device 100.

FIG. 2 is a schematic diagram illustrating the relationship between thefirst and second clock signals (CLK1, CLK2) in accordance with someembodiments. Each of the first and second clock signals (CLK1, CLK2)alternates between a low signal level, e.g., reference voltage (Vss)level, and a high signal level, e.g., twice the supply voltage (Vdd)level. In the example of the FIG. 2, the high signal levels of the firstclock signal (CLK1) and the high signal levels of the second clocksignal (CLK2) do not overlap with each other in time. That is, asillustrated in FIG. 2, there is a time (t1) between a falling/risingedge of the first clock signal (CLK1) and a rising/falling edge of thesecond clock signal (CLK2). As will be apparent from the discussionwhich follows, the time (t1) is determined to ensure that the durationthereof, e.g., about 0.5 μs, is long enough so that falling/rising edgesof the first clock signal (CLK1) and rising/falling edges of the secondclock signal (CLK2) do not overlap, preventing short-circuiting of thesupply node 110 and the reference node 120. The time (t1) is furtherdetermined to ensure that the duration thereof is short enough so thatthe load 190 is driven at a substantially constant load voltage(V_(LOAD)) by the voltage multiplier 140.

FIG. 3 is a flow chart illustrating an exemplary method 300 of operationof the device 100 in accordance with some embodiments. The examplemethod 300 is described with further reference to FIG. 1 for ease ofunderstanding. It should be understood that method 300 is applicable tostructures other than that in FIG. 1. In operation 310, the first switchunit 150 receives the first clock signal (CLK1) and the second switchunit 160 receives the second clock signal (CLK2).

After a time (t1), in operation 320, the first clock signal (CLK1)transitions from a low signal level to a high signal level and controlsthe first switch (SW1) to connect the first node (N1) to the supply node110 and the second switch (SW2) to connect the second node (N2) to thereference node 120. This connects the first capacitive element (C1)between the supply node 110 and the reference node 120, charging thefirst capacitive element (C1) to the supply voltage (Vdd). At this time,the second clock signal (CLK2) is at the low signal level and controlsthe third switch (SW3) to disconnect the second node (N2) from thesupply node 110 and the fourth switch (SW4) to disconnect the first node(N1) from the load node 130.

Next, the first clock signal (CLK1) transitions back to the low signallevel and controls the first switch (SW1) to disconnect the first node(N1) from the supply node 110 and the second switch (SW2) to disconnectthe second node (N2) from the reference node 120. After a time (t1), inoperation 330, the second clock signal (CLK2) transitions from the lowsignal level to the high signal level and controls the third switch(SW3) to connect the second node (N2) to the supply node 110 and thefourth switch (SW4) to connect the first node (N1) to the load node 130.This connects the first capacitive element (C1) between the supply node110 and the load node 130, providing a load voltage (Vload)substantially equal to the sum of the supply voltage (Vdd) and a chargedvoltage across the first capacitive element (C1) at the load node 130.This, in turn, charges the second capacitive element (C2) to the loadvoltage (Vload). As a result, the load 190 is driven at the load voltage(Vload) about twice the supply voltage (Vdd).

From an experimental result, at a given current, e.g., 400 uA, flowingthrough the load 190, the device 100 provides a substantially constantload voltage (Vload), e.g., about 91% to about 99% of two times thesupply voltage (Vdd), and a relatively small ripple voltage, e.g., about20 mV to about 30 mV. Further, the device 100 outputs the load voltage(Vload) within a short period of time, e.g., 8 Ξs, after the device 100receives the supply voltage (Vdd).

As noted above, capacitance of a capacitive element (e.g., C1) can beinfluenced by capacitive element construction. FIG. 4 is a schematicsectional view illustrating an exemplary first capacitive element (C1)in accordance with some embodiments. The first capacitive element (C1)includes a substrate 410, first and second well regions 420, 430, and atransistor 440. The substrate 410 has a p-type conductivity and isconnected to the reference node 120. The substrate 410 may includesilicon, germanium, other semiconductor material, or a combinationthereof. The first well region 420 is formed, such as by implantation,in a portion of the substrate 410. The first well region 420 may includethe same material as the substrate 410, but is doped with n-typeimpurities and thus have an n-type conductivity. FIG. 5 is schematicdiagram illustrating an exemplary equivalent circuit of the firstcapacitive element (C1) in accordance with some embodiments. As can beseen from FIG. 5, because the substrate 410 and the first well region420 have different conductivity types, the substrate 410 and the firstwell region 420 cooperatively form a diode (D1).

The second well region 430 is implanted in a portion of the first wellregion 420, includes the same material as the substrate 410, and has ap-type conductivity. The first well region 420 extends deeper into thesubstrate 410 than the second well region 430. As can be seen from FIG.5, because the first well region 420 and the second well region 430 havedifferent conductivity types, the first well region 420 and the secondwell region 430 cooperatively form a diode (D2) connected to the diode(D1).

The transistor 440 is over the second well region 430 and includessource and drain regions 440 a, 440 b that has an n-type conductivityand that are implanted in the second well region 430. The transistor 440further includes a gate region 440 c over a channel region between thesource and drain regions 440 a, 440 b. As can be seen from FIG. 5,because the source and drain regions 440 a, 440 b are connected to eachother and to the second node (N2), the first capacitive element (C1) isformed by the transistor 440. The second well region 430 is connected tothe second node (N2) so as not to leave the second well region 430floating. The first well region 420 and the gate region 440 c areconnected to each other and to the first node (N1). This results in anincreased capacitance for the first capacitive element (C1), e.g., about10% from a capacitance thereof when the first well region 420 and thegate region 440 c are disconnected from each other, without enlarging aphysical size of the first capacitive element (C1), improving anefficiency of the device 100, for as much as 12%.

FIG. 6 is a schematic diagram illustrating an exemplary device 600 inaccordance with some embodiments. This embodiment differs from theprevious embodiment in that the example device 600 further includes aclock generator 610 and a second voltage multiplier 620. The clockgenerator 610 is connected between a feedback node 630 and the referencenode 120 and includes first and second modules (not shown). The firstmodule, e.g., a cross-coupled flip-flop, is configured to receive aninput signal (IN) and to generate the first and second clock signals(CLK1, CLK2) that each correspond to the input signal (IN) and alternatebetween a low signal level, e.g., reference voltage (Vss) level, and ahigh signal level, e.g., level of a feedback voltage (Vfeedback) at thefeedback node 630. The second module is configured to introduce a delay,i.e., the time (t1), between a falling/rising edge of the first clocksignal (CLK1) and a rising/falling edge of the second clock signal(CLK2). In an implementation, the second module includes a pair ofinverters connected in series.

The voltage multiplier 140 is connected to the clock generator 610, isconfigured to receive the first and second clock signals (CLK1, CLK2)and, as described above, is controlled by the first and second clocksignals (CLK1, CLK2) so as to generate a load voltage (Vload) higherthan, e.g., about twice, the supply voltage (Vdd) for driving the load190.

The second voltage multiplier 620 is connected to the clock generator610, is configured to receive the first and second clock signals (CLK1,CLK2), and is controlled by the first and second clock signals (CLK1,CLK2) so as to generate the feedback voltage (Vfeedback) higher than,e.g., about twice, the supply voltage (Vdd) for driving the clockgenerator 610.

In further detail, a switch (D3), e.g., one or more diodes, is connectedbetween the supply node 110 and the feedback node 630. The switch (D3)connects the feedback node 630 to the supply node 110, e.g., is forwardbiased, when the feedback voltage (Vfeedback) is less than the supplyvoltage (Vdd), and disconnects the feedback node 630 from the supplynode 110, e.g., is reversed biased, when the feedback voltage(Vfeedback) increases to greater than the supply voltage (Vdd). In anembodiment, the switch (D3) includes one or more diode-connected FETs,any sort of diode, or other type of switch.

The second voltage multiplier 620 includes third and fourth nodes (N3,N4), third and fourth capacitive elements (C3, C4), and third and fourthswitch units 640, 650. The third capacitive element (C3) is connectedbetween the third and fourth nodes (N3, N4). In this embodiment, thethird capacitive element (C3) has a structure similar to that describedabove in connection with the first capacitive element (C1). The thirdswitch unit 640 includes fifth and sixth switches (SW5, SW6), isconnected to the clock generator 610, and is configured to receive thefirst clock signal (CLK1) that controls operations of the fifth andsixth switches (SW5, SW6). The fifth switch (SW5) is connected betweenthe supply node 110 and the third node (N3) and is operable so as toselectively connect and disconnect the third node (N3) to and from thesupply node 110. The sixth switch (SW6) is connected between the fourthnode (N4) and the reference node 120 and is operable so as toselectively connect and disconnect the fourth node (N4) to and from thereference node 120.

Similarly, the fourth switch unit 650 includes seventh and eighthswitches (SW7, SW8), is connected to the clock generator 610, and isconfigured to receive the second clock signal (CLK2) that controlsoperations of the seventh and eighth switches (SW7, SW8). The seventhswitch (SW7) is connected between the supply node 110 and fourth node(N4) and is operable so as to selectively connect and disconnect thefourth node (N4) to and from the supply node 110. The eighth switch(SW8) is connected between the third node (N3) and the feedback node 630and is operable so as to selectively connect and disconnect the thirdnode (N3) to and from the feedback node 630. In this embodiment, theswitches (SW5-SW8) are n-type FETs. In some embodiments, at least one ofthe switches (SW5-SW8) is a p-type FET. In other embodiments, at leastone of the switches (SW5-SW8) is any sort of transistor, e.g., a BJT, orother type of switch.

The fourth capacitive element (C4), e.g., a MOSCAP, a MIM capacitor, orother type of capacitor, is connected between the feedback node 630 andthe reference node 120.

As will be apparent from the discussion which follows, the time (t1) isdetermined to ensure that the duration thereof is long enough so thatfalling/rising edges of the first clock signal (CLK1) and rising/fallingedges of the second clock signal (CLK2) do not overlap, preventingshort-circuiting of the supply node 110 and the reference node 120.Further, the time (t1) is determined to ensure that the duration thereofis short enough so that the clock generator 610 is driven at asubstantially constant feedback voltage (Vfeedback) by the secondvoltage multiplier 620. FIG. 7 is a flow chart illustrating an exemplarymethod 700 of operation of the device 600 in accordance with someembodiments. The example method 700 is described with further referenceto FIG. 6 for ease of understanding. It should be understood that method700 is applicable to structures other than that in FIG. 6. In operation710, the switch (D3) connects the feedback node 630 to the supply node110.

In operation 720, the feedback node 630 receives a feedback voltage(Vfeedback) less than the supply voltage (Vdd), e.g., substantiallyequal to the difference between the supply voltage (Vdd) and a voltagedrop across the switch (D3). In operation 730, the clock generator 610receives an input signal (IN) and generates the first and second clocksignals (CLK1, CLK2). In operation 740, the third switch unit 640receives the first clock signal (CLK1) and the fourth switch unit 650receives the second clock signal (CLK2).

After a time (t1), in operation 750, the first clock signal (CLK1)transitions from a low signal level to a high signal level and controlsthe fifth switch (SW5) to connect the third node (N3) to the supply node110 and the sixth switch (SW6) to connect the fourth node (N4) to thereference node 120. This connects the third capacitive element (C3)between the supply node 110 and the reference node 120, charging thethird capacitive element (C3) to the supply voltage (Vdd). At this time,the second clock signal (CLK2) is at the low signal level and controlsthe seventh switch (SW7) to disconnect the fourth node (N4) from thesupply node 110 and the eighth switch (SW8) to disconnect the third node(N3) from the feedback node 630.

Next, the first clock signal (CLK1) transitions back to the low signallevel and controls the fifth switch (SW5) to disconnect the third node(N3) from the supply node 110 and the sixth switch (SW6) to disconnectthe fourth node (N4) from the reference node 120. After a time (t1), inoperation 760, the second clock signal (CLK2) transitions from the lowsignal level to the high signal level and controls the seventh switch(SW7) to connect the fourth node (N4) to the supply node 110 and theeighth switch (SW8) to connect the third node (N3) to the feedback node630. This connects the third capacitive element (C3) between the supplynode 110 and the feedback node 630, increasing the feedback voltage(Vfeedback) to substantially the sum of the supply voltage (Vdd) and thecharged voltage across the third capacitive element (C3). This, in turn,charges the fourth capacitive element (C4) to the feedback voltage(Vfeedback). In operation 770, the switch (D3) disconnects the feedbacknode 630 from the supply node 110 when the feedback voltage (Vfeedback)increases to greater than the supply voltage (Vdd). As a result, theclock generator 610 is driven at the feedback voltage (Vfeedback) abouttwice the supply voltage (Vdd), thereby enabling the clock generator 610to generate the first and second clock signals (CLK1, CLK2), each ofwhich alternates between a low signal level, e.g., reference voltage(Vss) level, and a high signal level, e.g., twice the supply voltage(Vdd) level.

As described above, the second voltage multiplier 620 enables the clockgenerator 610 to generate first and second clock signals (CLK1, CLK2)that have a high signal level greater than the supply voltage (Vdd)level. In some embodiments, method 700 further includes operations310-330 of method 300. In such some embodiments, the voltage multiplier140 uses the first and second clock signals (CLK1, CLK2) output by theclock generator 610 to generate the load voltage (Vload) greater thanthe supply voltage (Vdd) at which the voltage multiplier 140 operates.As such, in other embodiments, the voltage multiplier 140 may bereplaced with a circuit so long that it operates at a supply voltage(Vdd) and at a clock signal, a level of which is greater than the supplyvoltage (Vdd) level.

In an alternative embodiment where the load 190 is light and does notdraw as much load current as a heavy load, the device 600 does notinclude the voltage multiplier 140 and the load 190 is connected to thefeedback node 630. That is, in such an alternative embodiment, thesecond voltage multiplier 620 is configured to drive both the load 190and the clock generator 610 at a voltage greater than, e.g., twice, thesupply voltage (Vdd).

In an embodiment, a device comprises a capacitive element that iscoupled between first and second nodes and that includes a first wellregion, a second well region, and a transistor. The second well regionis formed in the first well region, has a different conductivity typethan the first well region, and is coupled to the second node. Thetransistor includes source and drain regions formed in the second wellregion and coupled to each other and to the second node, a channelregion between the source and drain regions, and a gate region over thechannel region. The first well region and the gate region are coupled toeach other and to the first node.

In another embodiment, a device comprises a clock generator and avoltage multiplier. The clock generator is coupled between a feedbacknode and a reference node and is configured to generate a clock signalthat alternates between a level of a feedback voltage at the feedbacknode and a level of a reference voltage at the reference node. Thevoltage multiplier includes a capacitive element and a switch unit. Thecapacitive element is coupled between first and second nodes. The switchunit is controlled by the clock signal so as to selectively couple thesecond node to a supply node and the first node to the feedback node,thereby increasing the feedback voltage to substantially the sum of asupply voltage at the supply node and a charged voltage across thecapacitive element.

In another embodiment, a method comprises: coupling a feedback node to asupply node; the feedback node receiving a feedback voltage less than asupply voltage at the supply node; generating a clock signal; and theclock signal controlling a switch unit to couple a capacitive elementbetween the supply node and the feedback node, thereby increasing thefeedback voltage to greater than the supply voltage.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A device comprising: a capacitive element coupledbetween first and second nodes and including a first well region, asecond well region formed in the first well region, having a differentconductivity type than the first well region, and coupled to the secondnode, and a transistor including source and drain regions formed in thesecond well region and coupled to each other and to the second node, achannel region between the source and drain regions, and a gate regionover the channel region, wherein the first well region and the gateregion are coupled to each other and to the first node.
 2. The device ofclaim 1, further comprising: a first switch unit operable so as toselectivity couple the first node to a supply node and the second nodeto a reference node, thereby charging the capacitive element to a supplyvoltage at the supply node; and a second switch unit operable so as toselectively couple the second node to the supply node and the first nodeto a load node, whereby a load coupled between the load node and thereference node is driven at a load voltage substantially equal to thesum of the supply voltage and a charged voltage across the capacitiveelement.
 3. The device of claim 2, further comprising a secondcapacitive element coupled between the load node and the reference nodeand configured to be charged to the load voltage.
 4. The device of claim2, further comprising a clock generator coupled to a feedback node andconfigured to generate first and second clock signals, each of whichalternates between a level of a reference voltage at the reference nodeand a level of a feedback voltage at the feedback node and controlsoperation of a respective one of the first and second switch units. 5.The device of claim 4, further comprising: a second capacitive elementcoupled between third and fourth nodes; a third switch unit controlledby the first clock signal so as to selectively couple the third node tothe supply node and the fourth node to the reference node, therebycharging the second capacitive element to the supply voltage; and afourth switch unit controlled by the second clock signal so as toselectively couple the fourth node to the supply node and the third nodeto the feedback node, thereby increasing the feedback voltage tosubstantially the sum of the supply voltage and a charged voltage acrossthe second capacitive element.
 6. The device of claim 4, furthercomprising a second capacitive element coupled between the feedback nodeand the reference node and configured to be charged to the feedbackvoltage.
 7. The device of claim 4, further comprising a switch coupledbetween the supply node and the feedback node and configured to connectthe feedback node to the supply node when the feedback voltage is lessthan the supply voltage and to disconnect the feedback node from thesupply node when the feedback voltage increases to greater than thesupply voltage.
 8. The device of claim 1, wherein the capacitive elementfurther includes a substrate, the first well region is formed in thesubstrate, and the substrate has a different conductivity type than thefirst well region and is coupled to a reference node.
 9. A devicecomprising: a clock generator coupled between a feedback node and areference node and configured to generate a clock signal that alternatesbetween a level of a feedback voltage at the feedback node and a levelof a reference voltage at the reference node; and a voltage multiplierincluding a capacitive element coupled between first and second nodes,and a switch unit controlled by the clock signal so as to selectivelycouple the second node to a supply node and the first node to thefeedback node, thereby increasing the feedback voltage to substantiallythe sum of a supply voltage at the supply node and a charged voltageacross the capacitive element.
 10. The device of claim 9, wherein theclock generator is further configured to generate a second clock signal,the voltage multiplier further includes a second switch unit controlledby the second clock signal so as to selectively couple the first node tothe supply node and the second node to the reference node, therebycharging the capacitive element to the supply voltage.
 11. The device ofclaim 10, further comprising: a second capacitive element coupledbetween third and fourth nodes; and a third switch unit controlled bythe second clock signal so as to selectivity couple the third node tothe supply node and the fourth node to the reference node, therebycharging the second capacitive element to the supply voltage.
 12. Thedevice of claim 9, further comprising: a second capacitive elementcoupled between third and fourth nodes; and a second switch unitcontrolled by the clock signal so as to selectivity couple the fourthnode to the supply node and the third node to a load node, whereby aload coupled between the load node and the reference node is driven at aload voltage greater than the supply voltage.
 13. The device of claim12, further comprising a third capacitive element coupled between theload node and the reference node and configured to be charged to theload voltage.
 14. The device of claim 9, further comprising a switchcoupled between the supply node and the feedback node and configured toconnect the feedback node to the supply node when the feedback voltageis less than the supply voltage and to disconnect the feedback node fromthe supply node when the feedback voltage increases to greater than thesupply voltage.
 15. The device of claim 9, wherein the capacitiveelement includes a first well region, a second well region formed in thefirst well region, having a different conductivity type than the firstwell region, and coupled to the second node, and a transistor includingsource and drain regions formed in the second well region and coupled toeach other and to the second node, a channel region between the sourceand drain regions, and a gate region over the channel region, whereinthe first well region and the gate region are coupled to each other andto the first node.
 16. The device of claim 9, further comprising a loadcoupled to the feedback node.
 17. The device of claim 9, furthercomprising a second capacitive element coupled between the feedback nodeand the reference node and configured to be charged to the feedbackvoltage.
 18. A method comprising: coupling a feedback node to a supplynode; the feedback node receiving a feedback voltage less than a supplyvoltage at the supply node; generating a clock signal; and the clocksignal controlling a switch unit to couple a capacitive element betweenthe supply node and the feedback node, thereby increasing the feedbackvoltage to greater than the supply voltage.
 19. The method of claim 18,further comprising: generating a second clock signal; and the secondclock signal controlling a second switch unit to couple the capacitiveelement between the supply node and a reference node, thereby chargingthe capacitive element to the supply voltage.
 20. The method of claim18, further comprising decoupling the feedback node from the supply nodewhen the feedback voltage increases to greater than the supply voltage.